The long-term goal of this project is to understand the signaling pathways that regulate microtubules and microtubule-dependent processes. The general hypothesis guiding this project is that cortical events activate signaling pathways that affect microtubule stability. This hypothesis stems from studies performed in the PI's laboratory on the effect of osmotic support on microtubules and their associated proteins, and fits well with the PI's long-term goals to better understand how the microtubule cytoskeleton is regulated. The main finding of the preliminary studies is that mutations in CinSp, a yeast microtubule-associated motor protein that functions in mitosis, compromise cell wall integrity and that osmotic support stabilizes microtubules and suppresses the temperature sensitivity phenotype associated with these mutations. An additional basis for the hypothesis is the identification of two multicopy suppressors, GIC1 and KRE6, which suppress the cin8 mutations and are associated with MAP kinase pathways that regulate osmotic conditions and cell integrity. How osmotic conditions affect microtubule stability through interaction with signaling pathways is not known and is the focus of this new project. The clear suppression of the cin8 mutations by osmotic support provides an efficient tool for identification of components of the pathways that are induced by osmotic conditions. The specific aims in this proposal will test the hypothesis by studying the effect of osmotic stabilizers on the microtubule cytoskeleton and elucidating the signaling pathways that affect microtubule stabilization. Three experimental approaches will be used to test the hypothesis. In Aim 1, microbial, biochemical, molecular and cell biology techniques will be employed to assay the effect of osmolytes on microtubule dynamics and function. In Aim 2, mutational analysis will identify genes that participate in osmotically-induced signaling pathways that stabilize microtubules. In Aim 3, epistasis analysis of these genes will be used to construct models for the cascade of events that affect microtubule stability. Results obtained under this project will enhance our current knowledge on how cells regulate their microtubules and will significantly impact the fields of cytoskeleton and signal transduction. Because some cancer therapeutic drugs are based on controlling microtubule stability, new information on such mechanisms could be applied to the search of new drugs that target components of pathways that regulate microtubule stability in cancerous cells.